Flour milling process



Sept. 26, 1961 Z` BLOCK ET AL FLOUR MILLING PROCESS Filed NOV. 20, 19574 Sheets-Sheet 2 Tlc'A- ATTORNEY Sept. 26, 1961 z. BLOCK ET AL 3,001,727

FLOUR MILLING PROCESS Filed Nov. 20, 1957 4 Sheets-Sheet 5 INVENTORSzum: auch; wALrsR/V- 94ers ATTORNEY Sept. 26, 1961 z. BLOCK ET Al.

FLOUR MILLING PROCESS Filed Nov. 20, 1957 4 Sheets-Sheet 4 INVENTORzaNAL BLog/m wn T H. I AME A f mj/Jaa Hmz,

ATTORNEY United States Patent G FLOUR MILLING PROCESS Zenas Block,Larchmont, and Walter H. Harte, White Plains, N.Y., and James F. Walsh,Daytona Beach, Fla., assignors to DCA Food Industries Inc., New

York, N.Y., a corporation of New York Filed Nov. 20, 1957, Ser. No.697,717 2 Claims. (Cl. 241-9) The present invention relates -generallyto an improved process for the production of our, and it relates moreparticularly to an improved flour milling process.

The principal function of the milling of wheat to produce flour is theseparation of the endosperm from the husk and germ of the wheat berry.This is generally done by breaking the berries and separating the branfrom the endosperm and subjecting the endosperm particles to successivereductions, siftings and puriications to reduce the endosperm to tlourand separate the bran and germ. Conventionally, the wheat is Ifirstcleaned and conditioned and fed to a set of corrugated break rolls thedischarge of which is passed through a series of sieves from which thetopmost tailingsnare fed to a successive hner break roll, the.intermediate semolina and middlings to puriers and reduction rolls andthe throughs to the clear stream. There are usually three to ve breakrolls fed in succession as aforesaid. There are likewise several sets orrolls, eight in the popular Hungarian system, each having a purifier atits feed end and a sifter gang at its discharge end.

The throughs of the sifters and purifiers form tiour of variouscompositions whereas the tailings and middlings' are conveyed to furtherprocessing or discharged as a bran or feed. There are thus a pluralityof streams emerging from the mill which are mixed in the desired mannerto produce straight our, patent our, clears, feed of variouscompositions, etc. The composition and baking properties of the endproduct are dependent, for practical purposes, only to a slight degreeon the milling procedure and to a major extent on the type of wheatbeing processed. The flour from the various streams dider little intheir protein or gluten content, those with maximum protein contenteither being present in very low percentages or containing an excess ofundesirable ash indicative of the presence of bran.

ln the production of baked products, a high gluten, low bran contenttlour is required for bread and other yeast raised products, whereas arelatively low gluten our is desirable for cakes, cookies, biscuits andother chemically leavened products. In the conventional millingprocesses the composition of the flour and its usefulness for bread orcake are determined for the most part by the kind of wheat being milledand only to a minor extent on the milling procedure. Thus, a soft wheatwill not produce a satisfactory bread flour because of its low proteinlevel whereas its produces 'a highly satisfactory cake flour. A hardwheat', on the other hand, being high in gluten, produces a Satisfactorybread flour. The protein content of wheat, depending on the species,source and other conditions, yvaries between about 8% and 15% and theprotein content of commercial ilours Varies between 8% and 14%. Thewheat endosperm contains, in addition to the protein which serves as acementing matrix, a

ECC

major portion of starch in the form of granules having diameters ofbetween 2 microns and 50 microns, the majority of lgranual sizes beingat opposite ends of the spectrum with Ivery few in between.

'In milling the ilour, rupture or breaking of the starch granulesadversely aifects the properties of the flour. The protein is dispersedthroughout the endosperm, being more concentrated at the surface thereofadjacent to the husk. The particle size of the commercial ours generallyranges between about l5 and 150 microns.

it is apparent from the above that the conventional milling process ishighly inflexible providing a flour whose optimum characteristics anduse are determined by the wheat feed. Moreover, the equipment employed,particularly in the breaking, reducing, sifting and purifying steps isextensive and complex, requiring critical adjustments and being highlypower consuming.

An analysis of the protein and ash content of hours in accordance withthe particle size indicates that the protein and ash content vary to alimited degree, with the particle size. By tsing advantage of thisprotein and ash distribution these components of the ilour may be i11-creased or diminished, but only to a very limited extent and in ainterdependent nature.

it is thus a principal object of the present invention to provide animproved process for the production of flour.

Another object of the present invention is to provide an improvedprocess for the milling of our.

A further object of the present invention is to provide an improvedprocess for the milling of ilour capable of substantially enhancing andimpoverishing selected fractions of the flour.

Still a further object of the present invention is to provide animproved process for the milling of flour capable of producing from alow protein wheat a high protein hour suitable for the 'production ofbread and other yeast raised products.

Another object of the present invention is to provide an improvedprocess for the milling of our, said process being characterized by :its`great versatility and flexibility.

Still another object of the present invention is to provide an improvedmethod for the milling of our characterized by the use of standardequipment.

The -above and other objects of the present invention will becomeapparent from a reading of the following description, taken inconjunction with the accompanying drawings, wherein:

FIGURE l is a graph illustrating the protein versus particle size`distribution in conventionally milled soft wheat flour;

FiGURE 2 is a graph illustrating the protein versus particle sizedistribution of a soft wheat our subjected to attrition comminuting of atype employed in the present invention, the attrition mili having itsthrowout mechanism deactivated as will be hereinafter set forth;

FIGURE 3 is a graph of the protein versus particle size distribution ofa soft wheat flour subjected to the method of attrition in accordancewith the present invention, the throwout mechanism of the attrition millbeing adjusted to throwout as will be hereinafter set forth;

FIGURE 4 is a llow diagram illustrating an example of the method ofprocessing soft wheat flour in accordance with the present invention;

FIGURE is a'front elevational view of a mill classifier employed inpracticing the present invention;

FIGURE 6 is a detail sectional-view taken along line 6 6 in FIGURE 5;

FIGURE 7 is a transverse sectional view of an aerodynamic particleclassier employed in the present process; and Y yFIGURE 8 is a sectionalview taken along vline 8 8 in FIGURE 7.

The present invention is :based on the discovery that when airborneyfragments of a cereal endosperm are circulated in va closed path andcomminuted while so circulated, linely comminuted particles beingcontinuously separated from the main stream and coarse particles beingcontinuously separated from the main stream at a predetermined raterelative to the feed of the endosperm fragments into the stream, thetine particles are enriched in their protein content to a degree notheretofore experienced or obtainable by the conventional millingprocess. The present invention therefore contemplates an improvedprocess vfor the milling of ilour comprising circulatingairbornefragments of a cereal endosperm in a closed path; comminutingsaid airborne fragments; continuously removing :fine comminutedparticles below a predetermined size from said closed path; continuouslyintroducing cereal endosperm fragments into said closed path at apredetermined rate of feed; and continuously withdrawing coarseparticles at a predetermined rate from said closed path, said lineparticles having =a higher Y protein concentration than said coarseparticles.

V'employed an attrition mill and air classifier known as the Raymondvertical mill which is provided with a cyclone separator and isproducedby the Raymond Division of Combustion Engineering, Inc., and anaerodynamic air separator known as the Mikroplex spiral air classifier,which is produced by the Alpine Company of Augsburg, Germany. Adescription of the -above apparatus 'and their operation will behereinafter `set forth. It should be pointed out that equipment of asimilar nature may be employed `where such equipment effects the novelprocess steps. The mill is characterized in that it causes a circulationof the treated material, continuously removing particles below apredetermined size therefrom and continuously removing coarse particlesat a predetermined rate. During the circulation of the treated materialit is subjected principally to -an interparticle attrition `and airparticle attrition. The spiral air classifier is a vortex type separatorin which a sharp cut and au adjustable line cut vsize may be achieved. Y

The following procedure is given merely yby way of example in thetreatment of straight flour derived from soft wheat, it being understoodthat the process may be varied over wide ranges tofrem'ploy Vas startingmaterial a hard Wheat ilour, middlings, semolina, or other materialderived from various sources and that the composition of the end productmay be varied by 'suitable adjustment and arrangement of the equipment,as will become apparent to those skilled in the art. o

As an example of the present process as applied to the treatment of ourderived fromsoft wheat, a straight Va nominal cut off point of about 2lmicrons.

flour having a 9.6% protein and an 0.42% ash content and a particle sizerange of between 6 and 100 microns was employed. The flour was derivedfrom a conventiona1 Hungarian system type flour mill in which the flourderived from the major streams possessed the following analysis:

Flour mill stream analyses The comminuting and classifying apparatus wasarranged and connected in a manner illustrated in FIG- URE 4 ofthedrawing, the classifiers being the Mikroplex air classifierabove-identified including a cyclone air separator, and the attritionmill being the Raymond vertical mill, including the separating systemassociated therewith, likewise above-identified. The straight soft wheatflour, as above set forth, is Afed into a rst classifier 1 adjusted to anominal cut ol point at about 13 microns. The lines from the classifier1 are directed to an outlet stream 1l) and the coarse'from theclassifier 1 is fed to the inlet of a second classifier 2. Theclassifier 2 is adjusted to a nominal cut point of about 42 microns. Thefines from the air classifier 2 are fed to a third yair classifier 3 andthe coarse from the air classifier 2 are fed to an attrition mill 4. Theair classifier 3 is'adjusted to a nominal cut off point of about 25microns. The coarse from the classifier 3 is delivered to a dischargestream 12 and the lines are fed to the attrition mill 4. VIt should benoted that the blade settings given in the following table are thecalibration indications employed on the aerodynamic air classifyingdevice hereinafter described in detail and specilieally identified, andeffect the correspondingly specified cut-olf points.V

The attrition mill 4, a Raymond vertical mill, includes upper and lowerrotating arms which effects a classification of the circulating airbornematerial and a set of mill arms which effects the attrition of thecirculating material in a manner as will be hereinafter set yforth ingreater detail. There are provided twelve lower classifying arms,twenty-four upper classifying arms and four upper mill arms. Thescalping or throwout mechanismfwas adjusted to remove of the material-fed to the mill 4. The fines from the attrition mill 4 are delivered tothe discharge stream 10, whereas the throwout is fed to a fourth airclassifier 5, the blades of which are set to produce The lines from theair classifier 5, are delivered to a discharge stream 11 and the coarseto a lifth air classifier 6 adjusted to a nominal cut off point oflabout 34 microns. The coarse from the air classifier 6 is fed to thedischarge stream 11 and the fines to the discharge stream 12.

The following table sets forth the protein and -ash content, particlesize range and Weight percentage of the various streams in theabove-described process as applied to the aforesaid soft fwheat flour:

Percent- Percent- Particle Step Machine and Approximate Settings age ofage Pro- Percent- Size,

Original tein age Ash Microns Feed Feed-Straight Soft Flour 100 9. 60.42 6-100 1 Air Classier l-Blades set at 30 Fines-To High ProteinProduct Stream 10 5 17. 0 0. 72 L15 Coarse-To Air Classier 2 95 9.2 0.4010-100 Feed-Coarse from Air Classier 95 9. 2 0. 40 10-100 2 AirOlassitier 2-Blades set at 45 Fines-To Air Classitier 3 30 6. 7 0. 4010-50 Coarse-To Attrition Mill 4--.-- 65 10. 5 0. 40 35-100 Feed-FinesFrom Air Classilier 2 30 6. 7 0. 40 10-50 3 Air Classier 3-Blades set at35 Fines-To Attrition Mill 4 15 9.9 0.47 10-30 Coarse-To Low ProteinProduct Stream 12 15 3. 5 0.33 20-50 4 Attrition Mill 4-12 BottomClassiier Feed-Coarse from Air Classier 2 and Fines from 80 10.4 0.4210-100 Arms 43; 24 Top Classifler Arms 44; Air Classitier 3.

4 Top Mill Arms 40; 0 Bottom Mill Fines-To High Protein Product Stream10 16 22.0 0.70 1-12 Arms 40 (Figure 6 of Drawings). Coarse To AirClassier 5 64 7. 35 0. 35 itl-50 Feed-Coarse Throwout from Attn'tion M64 7. 35 0.35 10-50 5 Air Classier 5-Blades Set at 32 Fines-T0Mid-Protein Product Stream 11. 24 8.1 0.40 10-22 Coarse-To Air Classier6 40 6.9 0. 32 20-50 Feed-Coarse from Air Classier 5 40 6.9 0. 32 20-506 Air Classifier 6Blades set at 40 Fines-To Low Protein Product Streaml2 15 3. 5 0. 30 20-35 Coarse-To Mid-Protein Product Stream 11 25 9.0 0.33 33-50 The high protein stream 10 constitutes 21% by weight of theoriginal feed and has -a protein content of 20.7%. 'Ihe discharge stream11 constitutes 49% by weight of the original feed and has an 8.6%protein content, whereas the discharge stream 12 constitutes 30% byweight of the original feed and has a 3.5% protein content.

The ilour fractions derived from the Various streams being of differentcomposition and characteristics are best suited for different purposes.Thus, the high protein our of the discharge stream 10 may be used inbreads, sweet doughs, yeast raised doughnuts, high protein foods and maybe employed in the protein enrichment of low -protein ours to permittheir use in breads and other .yeast raised products. The medium proteinflour fraction derived from the discharge Stream 11 may be used for cakedoughnuts, cakes, family flours and the like whereas the low proteiniiour fraction derived from discharge stream 12 may be used for cakes,crackers, cookies, wailies, pancakes, etc. It should be pointed out thatthe various streams may be mixed as desired or otherwise treated toachieve Hours of various desired characteristics. Moreover, the cutpoint of the air classiers may be varied as well as the comminutingaction of the mill and the percentage of throwout.

It has been found that by varying the percent ot throwout of the millthe protein distribution is varied. While the throwout may be dispensedwith, it is preferable to employ the mill throw so that between 15 and85% of the feed is removed by the throwout and the fines fraction has aparticle size below 30 microns. The use of the throwout is highlydesirable in that an increase in overall capacity is etfected with asimilar protein enrichment eifect, the classier capacity requirments arereduced, there is a reduction in the tendency to overcomminute the Hourwhich may result in a rupturing of the starch granules thereby reducingthe our quality and there is a reduction in the tendency to overheat theflour. If no throwout is employed and the input to the mill 4 is the35-100 micron fraction of conventional soft wheat iiour constituting 80%of the original weight and the mill is adjusted so that the output is inthe 3-40 micron range, the output may be aerodynamically separated asabove into a tine fraction of 3-21 microns constituting 35% of the feedand having a protein content and a coarse fraction of 15-40 micronsconstituting 65% of the feed and having a 5.8% protein content.

In FIGURES l to 3 of the drawing there are illustrated the proteinconcentration distribution graphs of various flour fractions inyaccordance with the particle size of the our fractions and thepercentage of the total our of each of these actions, in FIGURE 1 in thecase of a straight soft ilour of the type treated in accordance withconventional milling practice; in FIGURE 2 said our treated in theattrition mill above-identied and adjusted as above set forth with nothrowout; and as illustrated in FIGURE 3 in the same mill similarlyadjusted except that the throwout is activated so as to discharge of thefeed. It should be noted that in the conventionally milled llour thefraction having la particle size range Ibetween approximately 44 and 100microns constitutes approximately 65% of the flour and averagesapproximately 10% protein. The fraction between about 1S and 44 micronshas about 31/2 protein and constitutes about 15% of the llour. Thefraction between 8 and 18 microns particle size contains approximately10% protein and constitutes 15% of the flour and the fraction between 6and 8 microns accounts for the remaining 5% of the our and has a proteincontent of approximately 17%.

When the flour is treated in a comminuting mill, adjusted in the manneremployed in the above example, and the throwout mechanism inactivated, aradical redistribution of the protein is effected. Approximately 25% ofthe our is in the 3 to 8 micron particle size range and has a proteincontent between 20 and 22%; about 61/2% of the iiour is in the 8 to 9micron particle size range and has a protein content of approximatelyl41/2%; 18% of the flour is within the 9 to 10 micron particle sizerange and has a protein content of about 91/2%; and the remaining 50% ofthe our is within the 10 to 44 micron range and has a protein content ofapproximately 4%. When the throwout is activated so that the dischargerate thereof is about 80% of the feed rate of the flour to the mill, aprotein redistribution is effected in which the ilour fraction in the 4to 6 micron range constitutes 10% of the flour and has a protein contentof 24%; the 6 to 8 micron range constitutes about 16% of the flour andh-as a protein content between 14 and 18%; and about 2% of the flour isin the 8 to l0 micron range and has a protein content of approximately10%. The our fraction within the 10 to 44 micron rang-e constitutesabout 27% of the Hour and has a protein content between 4 and 5%, andthe remaining 45% of the our is within the 45 to 80 micron particle sizerange and has a protein content of 8%.

It should be noted that the protein distribution curves of the ourmilled in the comminuting mill without the throwout and with thethrowout have dilferent overall shapes. Where the throwout is notemployed the protein concentration increases at a somewhat uniform rateinversely as the particle size, Whereas where the throwout is employedthe protein concentration decreases with the decrease in the particlesize from 80 to 10 microns and thereafter increases sharply from the 10to 4 micron particle size range. The protein distribution of the varionsflour fractions where the throwout is employed permits, for practicalpurposes, a range'of blending and a versatility no less than thatafforded when the throwout is inactivated. However, the use of thethrowout is accompanied by the many advantages previously set forth.

Referring now to FIGURES and 6 of the drawings which illustrates thecomminuting mill and the associatedcyclone separator employed therewithin the present process, the numeral 2t) generally designates a basemember supportingv the mill main housing 21 upon a plurality of legs 22.The housing 21 is of vertical cylindrical conthrough an opening in theinclined wall 24 below the gen figuration including a lower or millingvcompartment 23 ment 23 to delineate a lower intermediate compartment,-

29. An annular ange 30 is directed inwardly fromthe Wall of the housing21 above the upper ring 28 to denne the upper'wall of an upperintermediate compartment 32 and the lower wall of an air impellercompartment 33. The upper and lower end walls of the housing 21 havealigned axial openings formed therein through which project the upperand lower ends of a main shaft 34. Suitably mounted water cooledbearings 36 rotatably supportV the shaft 34, the lower end of the shaft34 carrying a pulley 37 which is connected by way of a drive belt to acorresponding pulley carried on the drive shaft of a main drive motor 38mounted on the base 20.

Carried bythe shaft 34 in the compartment 23 directly above the inclinedwall 24 are three vertically spaced hub discs 39 which carry betweentheir opposing faces removable circumferentially spaced, radiallyprojecting mill arms 40 which extend to a point short of the wall of thehousing 21, the lower of themill arms 40, shown in broken line, beingremoved in the specificrexample given above. Lower, and upper pairs ofvertically spaced hub discs 41Vand 42 respectively are mounted on theshaft 34 Vand are substantially coplanar with the rings 27 and 28.

Each pair of hub discs 41 and 42 removably support circumferentiallyspaced, radially projecting lower and 'upper classifier arms 43 and 44,the end faces of which are downwardly outwardly inclined and areslightly spaced from and confront the parallel faces of the respectiverings 27 and 28. In the example of the improved process set'forth abovethere are provided four upper regularly, circumferentially spaced uppermill arms 40 and no lower mill arms 40, and there are provided twelvelower classiiier arms 43 and twenty-four upper classifier arms 44.

In FIGURE 6 of the drawings, the normal position of the removed bottommill arms 40 is illustrated in broken mes.

Carried along the lower inner border of Vthe annular partition 30 are aplurality of vertical, stationary guide vanes 46 the inner ends of whichare spaced from the surfaceV of the shaft 34. Disposed in thecompartment V33 and carried on the shaft 34 is an impeller 47 ofconventional structure. Y Formed in the peripheral wall of the uppercompartment 33 isan exit opening 48 affording entry into a tangentiallyextending conduit 5t) which is connected by suitable ducts 51v to theinlet of a cyclone air separator 52 of any well known construction. Thecyclonevseparator 52 is provided with an upper axial air outlet pipe 53which is connected by way of suitable duct Work to the mill air feedcompartment 26. A discharge pipe 54- communicates with the bottom of thecyclone separator 52, the flour emerging therefrom being delivered forfurther processing as desired.

Supported on the housing wall 21 and passing through the wall thereofinto the upper part of the comminuting compartment 23 is a feed pipe'56provided with a communicating feed hopper 57. Extending axially of thefeed pipe 56 is afeed screw or worm 58 having a shaft projectingrearwardly through an outer end wall of the feed pipe 56 andY carrying asprocket wheel 59. The sprocket wheel 597m turn is connected' by way ofa sprocket chain to the shaft of a variable speed reducing unit 60driven by a motor 61 mounted on the base 2G. The throwout mechanismincludes a tube 63 entering the lower portion of the commutingcompartment 23 communicating arms 46 and is provided with a dependingdischarge pipe or spout 64. A screw 65 extends along the length of thetube 673 and is provided at its outer end with a sprocket wheel 66connected to a variable speed drive 66a by means of a suitable sprocketchain.

In operation, the shaft 34 is driven at a high speed by means of thedrive motor 38. The impeller 47 circulates air throughV the opening inthe air feed compartment 26 upwardly through the housing 21 and thenceoutwardly through the duct 51. The air emerging from the duct 51Vtravels tangentially into the cyclone separator 52 to form a vortextherein, the air emerging through the duct 53 and returning to thecompartment 26. The solid material carried by the air stream enteringthe cyclone separator 52 drops through the lower duct 54'. Thecomminuting arms 40 impart a high circular motion to the air Within thecompartment 23 which effects a comminution of any particles carried inthe air stream, principally by interpanticle attrition and air particleattrition. The material to be comminuted is delivered by way of thehopper 57, feed tube 56 and worm 58 into the upper part of thecomminuting compartment 23 -Where it drops into the commuting zone atthe lower part of the compartment. `VThe line particles, eitherdelivered to the compartment 23 or produced by the comminuting actiontherein, are carried by the upward flow of the air through the spacesbetween successive rotating classifying blades 43 and 44. Thecentrifugal force imparted to the tine particles is insuflicient todivert them from their upward passage between the blades 43 and 44.However, the heavier particles having a greater centrifugal force`imparted thereto relative to the'upward drag of theV air are carriedoutwardly and drop downwardly to be eventually returned to thecomminuting compartment 23. Thus, the airborne particles arerecirculated 'in a closed path, those particles below a predeterminedsize'passing upwardly and outwardly-and the heavier particles beingreturned to thecomminutng zone.v The line particles which pass betweenthesuccessive blades 43 and 44'are carried upwardly and dischargethrough the opening in the impeller compartment 33 from which they arecarried to the cyclone separator 52 separated from the transporting airand discharged through the conduit 54. The coarse particles, on theother hand, are removed from the compartment 23 by the throwoutmechanism including they worm 65. Y. The ratio between the feed rate andthe coarse discharge rate may be adjusted to any desired value,

The airclassier employed in the example of the processV set forth aboveis illustrated in FIGURES 7 and 8 of the drawings and includes arelatively shallow cylindrical body member or housing 70 having an endwall 71 provided with a centrally located apertured boss 72 throughwhich extends an impeller drive shaft 73 driven at a high Velocity by aconventional motor. The housing 70 is divided into two sections by aninwardly directed outer annular-flange74 and an inwardly directedintermediate annular ange 76, the two resulting sections dening animpeller housing 77 and a separating compartment 78 respectively. Itshould be noted that the housing 70 includes volutes 7 9 and 80communicating peripherally with the compartments 77 and 7S respectively.

Formed integrally with the housing 70 is a first tangentially disposedduct 81 which' communicates with the separator compartment 78 'and anoutlet duct82 communicating with the impeller compartment 77 andtangential thereto. A feed passageway 83 is formed along the inner wallof the duct 81 and is separated from the remainder of the duct by anintegrally formed wall 84. An axially extending cylindrical cavity 86 isformed in the enlarged wall 87 of the housing 70 which is disposedwithin the separator compartment 78 adjacent to the feed passageway 83,the cavity 86 having a transverse entrance 19? 3.8 ,formed therein whichslot is directed tangentially 9 in a countercloclrwise direction, asseen in FIGURE 8 of the drawing, relative to the axis of the housing ata point spaced radially outwardly of the inner edge of the flange 76. Aconduit 89, in alignment and communicating with the cavity 86, isprovided with a worm 90 extending for the length of the conduit 89andthe cavity 86. The Worm 9) is driven by any suitable means so thatany material lodging in the cavity 86 is transported into the conduit 89and discharged through a spout 91.

A shaft 92 of reduced cross section extends coaxially from the mainshaft 73 and carries at its inner end a disc 94 which closely confrontsthe inner face of the housing end wall 71 and at its outer end a disc 96coplanar with the flange 74 and extending substantially to the inneredges of said ange 74. A plurality of radially extending impeller blades97 of conventional configuration are mounted on the inner face of thedisc 94 and extend to a point short of the shaft 92. An annular member93 is secured to the edges of the impeller blades 97 opposite the disc94 and is provided with an annular step 99 in its outer face registeringwith the flange 76. 'I'he central opening 100 formed in the annulus 98is provided with oppositely directed beveled edges.

A plurality of axially extending circumferentially spaced vanes 102 aredisposed within the classifying compartment 78 and are provided withshafts 103 passing through corresponding openings formed in the outerilange 74. The vanes 102 are provided with sharp downstream edges 104and are directed inwardly in a clockwise direction as illustrated inFIGURE 8 of the drawing. The angles of the blades 102 with thecircumference of the housing are concurrently adjustable, as shown inbroken line, by any suitable means engaging the blade shafts 103.

The cut oit point; that is, the particle size above and below whichseparation is effected, may be varied by adjusting the angles of theblades 102. The outlet conduit 82 is connected to an air or dustseparator of any conventional type, for example, a cyclone separator,the air outlet of which is connected to the inlet conduit 81.

In operation, the impeller is rotated at a high velocity by way of theshaft 73 so that the air entering the classitier by way of the conduit81 travels along a helical path directed by the blades 102 through thecentral opening 100, the air thence being discharged by the duct 82 tothe air separator. The feed material is fed through the passageway S3and is likewise transported in a helical path by the vortex produced inthe separator compartment 78. T'he cut off point is determined by theequilibrium between the centrifugal force imparted to the airborneparticles and the inward air drag of the vortex. Where the centrifugalforce is greater than the drag of the air tending to carry the particlesthrough the opening 100, as is the case of particles above apredetermined size, these particles will traverse a path of relativelylarge radius and be carried through the slot 88 and transported -to thedischarge spout by the worm 86. In the case of the liner particles, onthe other hand, the air drag is greater than the centrifugal force sothat these particles traverse a path of decreasing radius which carriesthem through the opening 100 and through the discharge duct 82.

It should be understood that other classifiers and mills may be employedin the place of those described above. It is important, however, thatthe mill be ofthe type which effects an attrition of the airborneparticles in the manner previously described.

While there has been described and illustrated a preferred embodiment ofthe present invention, it is apparent that numerous alterations andomissions may be made without departing from the spirit thereof.

We claim:

1. An improved process for the milling of flour comprising recirculatingairborne fragments of a cereal endosperm in a closed path, comminutingsaid fragments while airborne, continuously removing substantially allof the line comminuted particles below a predetermined size from saidclosed path, continuously introducing cereal endosperm fragments intosaid closed path at a predetermined rate of feed, and continuouslywithdrawing coarse particles at a predetermined rate from said closedpath, said tine particles having a higher average protein concentrationthan said coarse particles and defining a main constituent 0f the highprotein inished product stream of said milling process, said neparticles not exceeding substantially 12 microns in size, the ratio ofthe rate of withdrawal of said coarse particles to said rate of feedbeing approximately :100.

2. An improved process for the milling of flour comprising recirculatingairborne fragments of a cereal eudosperm in a closed path, comm-inutingsaid particles while airborne, continuously removing substantially allof the line comrninuted particles below a first predetermined size fromsaid closed path, continuously introducing cereal endosperm fragmentsinto said closed path at a predetermined rate, continuously withdrawingcoarse particles at a predetermined rate from said closed path, saidtine particles having a higher average protein concentration than saidcoarse particles, subjecting said withdrawn coarse particles outsidesaid closed path to an aerodynamic classification thereby to separatesaid coarse particles into a coarse traction and a ne fraction above andbelow a second predetermined particle size, and subjecting said coarsefraction to an aerodynamic classication to separate the particlestherein into coarse and ne subfractions above and below a thirdpredetermined particle size greater than said first predeterminedparticle size, said ne comminuted particles removed from said closedpath entering a first mill stream having a high protein content and saidcoarse subfraction having an intermediate protein concentrationapproximating that of said cereal vendosperm and entering a secondstream.

References Cited in the le of this patent UNITED STATES PATENTS1,535,120 Kanowitz et al Apr. 28, 1925 1,943,817 Dunton Ian. 16, 19342,200,822 Crites May 14, 1940 2,381,351 Hardinge Aug. 7, 1945 2,464,212Carter Mar. 15, 1949 2,501,622 Smith Mar. 21, 1950 2,509,919 GruenderMay 30, 1950 2,561,388 Lykken et al July 24, 1951 2,561,564 Crites July24, 1951 2,651,470 Dodds Sept. 8, 1953 2,752,097 Lecher June 26, 19562,774,476 Doyle Dec. 18, 1956 2,846,151 Wehn et al Aug. 5, 19582,883,309 Bernheim Apr. 21, 1959 FOREIGN PATENTS 640,561 Great BritainJuly 26, 1950 OTHER REFERENCES Flour Milling Processes, by I. E. Scott,1951, published by Chapman and Hall, Limited, 39 Essex St., W.C. 2,London, England, pages 409 to 411.

German Report on the Internationaler Brotkongress, laSrglburg, 1955,pages 154-157, Conference May 22-27,

Der Mikroplex-Spiralwindsichter-usw in Die Starke by H. Rumpf et al.,June 1952, pages 162-165.

